Final answer:
The mass of the spring would likely alter the equilibrium position because the additional mass impacts the system. A pendulum's frequency would decrease on the moon due to lower gravity. Lastly, an increase in the period of a wave results in a decrease in its frequency. So, the correct option is D.
Step-by-step explanation:
If the mass of the spring is taken into account in calculations, the most likely effect would be an alteration in the equilibrium position. The mass of the spring itself adds to the total mass that the spring must support, which affects the system's dynamics. If we were to consider the spring's mass, the additional mass would cause the spring to stretch further under gravity, resulting in a change in the equilibrium position. When evaluating a pendulum transported from Earth to the moon, its frequency would decrease due to the lesser gravitational acceleration on the moon (g). The frequency of a pendulum is inversely proportional to the square root of the acceleration due to gravity, thus with a smaller g on the moon than on Earth, the pendulum will oscillate more slowly.
Regarding wave characteristics, when the period of a wave increases, its frequency decreases since frequency is the inverse of the period. Thus, these two properties are inversely related.